This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-192815, filed Jun. 27, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a thin copper film directly bonded polyimide film used as a material of a flexible printed circuit board or the like and a method of manufacturing the same.
A polyimide film has high mechanical strength, high heat resistance, and good insulation properties. Therefore, a composite material combining this film with copper is used as a material of a flexible printed circuit board (FPC).
A polyimide film has low adhesion to copper. Hence, to combine a polyimide film with copper, a thin copper film (e.g., a copper foil) is adhered to the polyimide film via an adhesive. However, combining a polyimide film with a copper foil by an adhesive makes it difficult to decrease the thickness of a flexible printed circuit board as a final product owing to the presence of the adhesive layer. Also, the heat resistance of the flexible printed circuit board is limited by the heat resistance of the adhesive layer, and this limits the use of the product.
It is an object of the present invention to provide a thin copper film directly bonded polyimide film in which a thin copper film is directly and strongly connected to a polyimide film, and a method of manufacturing the same.
According to the present invention, there is provided a thin copper film directly bonded polyimide film comprising a polyimide film modified by bonding an organic silane compound having a cyano group represented by formula xe2x80x94Si(Rxe2x80x94CN)n (wherein R represents alkyl group having 1 to 6 carbon atoms and n represents a positive number from 1 to 3) to a carbon atom on a surface of the film, and a thin copper film directly bonded to the modified surface of the polyimide film.
According to the present invention, there is also provided a method of manufacturing a thin copper film directly bonded polyimide film, comprising the steps of:
activating carbon atoms of a surface of a polyimide film by subjecting the polyimide film to a plasma treatment, the activated carbon atoms being subsequently exposed to air atmosphere to allow to be bonded with oxygen to the active carbon atoms, thereby introducing an oxygen functional group into the surface of the polyimide film;
allowing a coupling reaction to take place between the oxygen functional group of the polyimide film and a silane coupling agent represented by formula (Rxe2x80x2O)(4-n)xe2x80x94Si(Rxe2x80x94CN)(wherein each of R and Rxe2x80x2 represents alkyl group having 1 to 6 carbon atoms and n represents a positive number from 1 to 3) to introduce an organic silane compound having a cyano group represented by formula xe2x80x94Si(Rxe2x80x94CN)(wherein R represents alkyl group having 1 to 6 carbon atoms and n represents a positive number from 1 to 3) to the carbon atoms on the surface of the polyimide film, thereby modifying the surface of the polyimide film; and
forming a thin copper film on the surface of the modified polyimide film by vacuum evaporation or sputtering of copper.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.